1. Field of the Invention
The present invention relates to a development device moving toner particles by a phase-shifting electric field, and a process cartridge and an image forming apparatus using the development device.
2. Discussion of the Background
An image forming apparatus of electrophotography has been known as a printer, a copier, a facsimile apparatus, a plotter, and a multi-function apparatus having the functions of a printer, a facsimile apparatus and a copier. The image forming apparatus forms an image on a recording medium by charging an image bearing member, forming a latent image on the charged image bearing member, developing the latent image into a toner image by causing toner particles as powder to be adhered to the latent image, and transferring the toner image onto the recording medium.
A known development device of such an electrophotographic image forming apparatus causes the toner particles to move in the horizontal and vertical directions on the surface of an electrostatic conveyance member by giving energy of a phase-shifting electric field to the toner particles. The toner particles are moved on the surface of the electrostatic conveyance member to a development area where the image bearing member and the electrostatic conveyance member oppose each other by the phase-shifting electric field and are caused to adhere to the latent image on the image bearing member in the development area. For example, Japanese Patent Publication No. 3530124 and Japanese Patent Laid-open publication No. 2004-198675 describe such a development device.
In a development device in which toner particles are moved by the phase-shifting electric field on the surface of an electrostatic conveyance member, to achieve uniform development, the toner particles must be supplied and moved uniformly throughout the whole development area of the electrostatic conveyance surface of the electrostatic conveyance member. Accordingly, it is important that the toner particles are uniformly supplied onto the electrostatic conveyance surface of the electrostatic conveyance member and the supplied toner particles are uniformly moved on the surface of the electrostatic conveyance surface of the electrostatic conveyance member.
However, when the electrostatic conveyance surface of the electrostatic conveyance member is formed in a circular shape, such as an endless loop and a roller, if the toner particles on the electrostatic conveyance surface pass the development area without contributing to development and return to a supply area of the electrostatic conveyance surface where toner particles are supplied from a toner supply device, even when the toner particles are uniformly supplied onto the electrostatic conveyance surface of the electrostatic conveyance member by the toner supply device, the quantity of toner particles moving on the electrostatic conveyance surface is not uniform, so that uneven development is caused.
In the development device described in JP No. 3530124, a collection member to collect the toner particles on the surface of an electrostatic conveyance member that have passed the development area of the electrostatic conveyance member is provided. However, the phase-shifting electric field causing the toner particles on the surface of the electrostatic conveyance member to move in the toner particle moving direction is generated in a collection area of the electrostatic conveyance member where the collection member is arranged, so that the toner particles that have not been collected when passing the collection area are moved by the phase-shifting electric field to reach the supply area of the electrostatic conveyance member where the toner particles are supplied, and thereby unevenness is caused in the quantity of the toner particles moving on the electrostatic conveyance surface of the electrostatic conveyance member.
Further, in an electrostatic conveyance member formed in a flat plate, if the toner particles on the electrostatic conveyance surface thereof that have passed the development area of the electrostatic conveyance member are not reliably collected, the toner particles stagnate at the downstream end part of the electrostatic conveyance member in the toner conveying direction, and it is likely that faulty movement of the toner particles is caused on the electrostatic conveyance surface of the electrostatic conveyance member.